Field assessment of parasitism on the New Zealand endemic Nyctemera annulata by Cotesia urabae: Can non-target impacts be ruled out?

Cotesia urabae is biological control agent (BCA) that was introduced in New Zealand in 2011 against the Eucalyptus defoliating lepidopteran pest Uraba lugens. During pre-and post-release host specificity testing, one non-target moth, the New Zealand endemic Nyctemera annulata, was occasionally attacked, albeit a poor physiological host for C. urabae development. With the BCA now established in the New Zealand environment, we undertook a sentinel larval trial in the field, which included artificial releases of C. urabae, to assess non -target impacts in habitats, either with or without the presence of the target host and its host plant. Approxi-mately two-thirds of all sentinel larvae released in the field were successfully recovered and reared in the lab-oratory to obtain parasitism. In the overlapping choice habitat (i.e., both target and non-target hosts present along with their host plants), the BCA C. urabae was recovered from 22.3% and 3.1% of target and non-target larvae, respectively. In the habitat devoid of Eucalyptus and its target larvae, C. urabae parasitised only 0.2% of the non-target, suggesting the BCA had immediately dispersed from release sites devoid of host cues. The non -target N. annulata was at greater risk of attack where the habitat overlap was most significant. This provided invaluable data to calibrate non-target risk models. Most importantly, the generalist parasitoids Diolcogaster perniciosus and Meteorus pulchricornis (Braconidae), which were also recovered in our field trials, had a much greater impact upon N. annulata than the specialist BCA.